Q: I've heard that an application built using static linking may run faster than a dynamic-linked application using shared libraries. I've also heard static linking is discouraged in Solaris 2. What should I do?

-- Linkless in La Crosse

A: Dynamic linking became the default for Solaris 1 in 1988 with the advent
of SunOS 4.0, and is, of course, the default for Solaris 2. It has several
advantages and, in many cases, offers better performance than static linking.

We'll start by examining the differences between static and dynamic
linking, then move on to the reasons why dynamic linking is
preferred. We'll also look at using dynamic linking to
improve application performance.

I mentioned the difference between interfaces and implementations last month,
but it is relevant so I'll repeat my definitions briefly:

Interfaces

Interfaces are the expression of "what" something does, and
are distinct from the implementation of "how" it is done. "How"
changes all the time, whereas the intent is to keep "what"
stable. Application stability and portability is available only
by defining and maintaining the relationship between an application
and the system in terms of the interfaces provided.

Implementations

The implementation hides behind the interface and does the actual
work. Bugfixes, performance enhancements, and underlying hardware
differences are handled by changes in the implementation. There are
often changes from one release to the next, or even from
one system to another running the same release.

Static linking


Static linking is the original method used to
combine an application program with the parts of various library
routines it uses. The linker is given your compiled code,
containing many unresolved references to library routines. It also gets
archive libraries (for example /usr/lib/libm.a) containing
each library routine as a separate module. The linker keeps working
until there are no more unresolved references and writes out a single
file that combines your code and a jumbled mixture of modules
containing parts of several libraries. The library routines make system
calls directly, so a statically linked application is built to work with
the kernel's system call interface.

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